The sternum is the trunk bone, which is located in the center of the front of the thorax and completes the human thorax together with the ribs on the left and right sides, the clavicle and the back side of the spine. In fact, except for the clavicle, scapula and pelvis, which are the upper and lower limb bones, all the bones of the trunk belong to the category of trunk bones. The sternum is a flat bone located in the front middle of the chest, divided into three parts from top to bottom: sternal stem, sternal body, and saber, the upper part of the chest is wider called sternal stem, the middle of the sternum is rectangular called sternal body, its lateral edge is connected with the second to seventh rib cartilage, the part where sternal body and sternal stem intersect, there is a transverse elevation to the front called sternal angle. The sternal angle flattens the second rib cartilage, which is an important marker for the rib count, and is also level with the lower edge of the fourth thoracic vertebra.